Metabolism

摘要

1 Let's get meta about metabolism: It's so much more than the thing you're trying to boost to banish those pesky extra pounds. The term refers to all of the chemical reactions within an organism that keep it alive. 2 Derived from metabolē, Greek for change, metabolism is about power: how it's acquired and how it's spent. Scientists have been using the word since the late 19th century, but the concept was around much earlier. 3 The 13th-century Arab physician Ibn al-Nafis, for example, observed that "both the body and its parts are in a continuous state of dissolution and nourishment, so they are inevitably undergoing permanent change." 4 Metabolism isn't just for individual organisms: Researchers apply the term to the processes through which entire natural ecosystems acquire and maintain (or lose) resilience, such as predator-prey balance and levels of photosynthesis. 5 Researchers also study the metabolism of some less-than-natural ecosystems — large cities — in terms of how urban areas consume resources and generate waste. 6 A primitive kind of metabolism was present in single-celled organisms more than 3.5 billion years ago. Due to low levels of atmospheric oxygen, the process may have been fermentative, still found in microbes such as yeast today. 7 As oxygen increased in Earth's atmosphere and organisms became more complex, different forms of metabolism evolved, from plants' photosynthesis to the lesser-known chemolithotrophy. 8 Many bacteria and archaea, another type of single-celled organism, use chemolithotrophy to get their energy from inorganic compounds such as ammonia in anoxic, extreme environments. No air, no sun, no problem! 9 Regardless of an organism's energy source, its metabolism is a balance of catabolism, breaking energy down into usable units, and anabolism, using those units for vital building projects such as bone growth. 10 The grunt work of metabolic processes is done by enzymes. These proteins act like crowd control, ensuring molecules reacting catabolically or anabolically are where they need to be. 11 The enzymes themselves are constantly losing stability and being replaced, which means metabolism is a product of ... metabolism. Whoa.